Reseller doesn't show up in the move-to list

I created a new reseller and would like to move a site to him. This is not possible, because the reseller doesn't show up in the move-to list. The Recycle bin is empty.
If I create another reseller the same happens again - not shown in the move-to list. The right's are not changed standard rights for resellers (which means: almost all rights except DNS stuff) and the quota of the site that is to move fits as well.

Where's my mistake? Or sth. wrong with the database? Thanks for help.
EDIT: version is ISPConfig 2.2.25

Oops, I see. What I wanted to do was to move a client (which was in fact a reseller, however) to a reseller account - what is done now, thanks
The trick is to change the group which a client belongs to. The webs are hiking along with the client.